Humans have applied scents and fragrances to their skins since ancient times. Originally, these aesthetically pleasing materials were commonly isolated in raw form as gums, resins or essential oils from their natural sources, such as the bark, roots, leaves and fruit of indigenous plants. These gums, resins and oils were directly applied to the body or were diluted with water or other solvent, including, in some cases, wine, then applied by means of the delivery vehicle. With the advent of modern chemistry, the individual components responsible for the odour properties of these resins, gums and oils were isolated and subsequently characterised, enabling the manufacture of “perfumes vehicles”, such as fine fragrances and aftershave lotions.
Traditional perfumes may comprise perfume oils derived from the sources discussed above and these oils may have a mixture of boiling points varying from low to high. It is self-evident that the highly volatile (low boiling), so-called “top note” constituents are short-lived once deposited onto a warm surface, such as skin. As a result, if a fragrance were entirely composed of such materials, it would not be very durable. In order to counter this and achieve increased fragrance substantivity and longevity, traditional perfumes tended to comprise high levels of lower volatility, so-called “middle note” and “base note” fragrance oils. This, however, has certain disadvantages: a consumer who tests a scent in a store often devotes only a short period of time to the evaluation, during which mainly the top notes of the scent will be in evidence, whereas, having purchased the product, that consumer may then be disappointed with the residual middle and base notes which were less in evidence during their test. In addition, the high volatility of top notes and their corresponding low longevity mean that they are traditionally included at low levels (since they are short lived)—a de facto restriction on the freedom of the perfumer to formulate a fragrance.
To counter these disadvantages of traditional perfumes, it has been proposed to generate complexes (hereafter “fragrance-releasing complexes”) of perfumes and other materials (hereafter “entrapment materials”), which depress the volatility of the fragrances and allow a more controlled release over time—reference is made to WO 99/21532. The production of such non-volatile complexes allows the perfume to be retained on skin/hair until such times as its release is triggered. Entrapment materials which have been proposed for complex formation in the prior art are discussed hereinbelow. The “trigger” referred to may be a single factor such as externally applied moisture or pH change, or, in the case of skin, a combination of factors such as sweat and its components—for example urea, lactic acid and moisture as well as sebum components, such as cholesterol.
At least in theory, the use of fragrance-releasing complexes allows the possibility of selectively retaining perfumes of a given volatility, such as the elusive top-note fragrances, thereby reducing or avoiding some of the disadvantages discussed in the above paragraphs. This would open up a world of new possibilities: not only could fragrances be designed to have longer lasting top notes, but the evolution of a fragrance post application could be changed to give unique character combinations during the so-called “dry down”, i.e. a uniquely changing character with time.
In practice, however, retention, particularly of the top-note scents, is not easy to achieve. While not wishing to be bound by any theory, there appear to be a number of reasons why this is so. In the first place, entrapment materials do not tend to differentiate between top, middle and bottom note fragrances, so that, in a given fragrance, all notes will be complexed. Put another way, increased perfume oil volatility does not appear to equate in any significant way to increased ability to complex. Rather, it would appear that, if all other factors are equal, the degree of complexation of a perfume raw material of given volatility is roughly proportional to its proportion in the mixture. To counteract this effect, it would, of course, be possible to increase the amount of top note oils present, but that could radically alter the oil balance, thereby changing the entire nature of the fragrance. It would also place significant restrictions on perfumers as to what they could put into their fragrances, similarly to the way that, in the past, the high volatility of top notes has lead to inclusion of low levels of top notes in fragrances. A second factor which may limit the capture and retention of top note fragrance oils by entrapment materials may be the presence in many traditional fragrances of certain non-aqueous solvents, such as certain alcohols, which may interfere with the entrapment materials.
Ideally, the present invention will achieve improved fragrance retention by fragrance-releasing complexes.
Ideally, the present invention will also selectively improve capture and retention of top note fragrances within fragrance-releasing complexes.
Ideally, the present invention will also provide personal care articles comprising compositions which achieve the above objectives.